GPT5 Model Support

[Winston-Hsiao]

Add support for GPT 5 series models.

ChatModelGPT5                             ChatModel = "gpt-5"
ChatModelGPT5Mini                         ChatModel = "gpt-5-mini"
ChatModelGPT5Nano                         ChatModel = "gpt-5-nano"

with config for adjusting reasoning level.

[Prhmma]

Almost have a PR ready for this

[Prhmma]

tested the python version locally, it works well, but please be aware because of the reason step, gpt-5 family are significantly slower and more expensive

[Winston-Hsiao]

tested the python version locally, it works well, but please be aware because of the reason step, gpt-5 family are significantly slower and more expensive

@Prhmma Is there a way to also make reasoning level adjustable for this flow? I've used GPT5Nano low and minimal reasoning effort (a lot cheaper and faster). And I am looking to use GPT5Nano low reasoning effort.

[Winston-Hsiao]

PR: #188

[Prhmma]

Thanks for the review Winston,
I've pushed changes for reasoning effort